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Peptide Hormones

Every Peptide Hormone in Your Body

13 min read|March 21, 2026

Peptide Hormones

5,700+ known peptide hormones

The HORDB database catalogs over 5,700 peptide hormones. The human body produces dozens of endogenous peptide hormones from at least 10 different organ systems, controlling everything from blood sugar to blood pressure to appetite.

Lugnier et al., Frontiers in Endocrinology, 2019

Lugnier et al., Frontiers in Endocrinology, 2019

Diagram showing human body organs that produce peptide hormonesView as image

Peptide hormones are the largest class of signaling molecules in human physiology. They range from 3 amino acids (thyrotropin-releasing hormone) to over 200 amino acids (growth hormone), and they regulate virtually every organ system. Unlike steroid hormones, which are lipid-soluble and pass through cell membranes, peptide hormones are water-soluble and act by binding cell-surface receptors, primarily G protein-coupled receptors (GPCRs).[1] For how these hormones coordinate digestion specifically, see our guide to gut peptide hormones.

Key Takeaways

  • The HORDB database catalogs over 5,700 peptide hormones across species; the human body produces dozens of endogenous peptide hormones from at least 10 organ systems
  • Peptide hormones are water-soluble, act via cell-surface receptors, and are rapidly degraded (half-lives of seconds to minutes), giving them precise temporal control over physiology
  • The hypothalamus-pituitary axis produces at least 15 peptide hormones that regulate growth, reproduction, stress, and water balance
  • The gut is the largest endocrine organ by cell count, producing GLP-1, GIP, CCK, secretin, ghrelin, PYY, and others that control digestion and appetite
  • The heart produces natriuretic peptides (ANP, BNP) that regulate blood pressure and fluid balance; BNP is used clinically to diagnose heart failure
  • Six GLP-1 receptor agonist drugs based on the endogenous incretin peptide GLP-1 have been approved for diabetes and obesity treatment (Ferrari et al., Am J Cardiovasc Drugs, 2022)

What makes a peptide hormone

A peptide hormone is any signaling molecule composed of amino acids linked by peptide bonds that is secreted into the bloodstream (or locally) to act on target cells at a distance. Three features distinguish them from other hormones:

Water solubility. Peptide hormones dissolve in blood plasma and do not require carrier proteins for transport, unlike steroid hormones. This means they act quickly, reaching target tissues within seconds of secretion.

Receptor-mediated signaling. Because they cannot cross cell membranes, peptide hormones bind extracellular receptors, primarily GPCRs, which trigger intracellular signaling cascades (cAMP, calcium, MAP kinase pathways). This two-step mechanism allows signal amplification: one hormone molecule can trigger the production of thousands of intracellular second messenger molecules.

Rapid degradation. Peptide hormones are cleared by peptidases in the blood and tissues, giving them half-lives measured in seconds to minutes. Insulin has a half-life of approximately 5 minutes. GLP-1 has a half-life of approximately 2 minutes. This rapid turnover allows precise, moment-to-moment regulation.[2] The short half-life is also the reason oral peptide delivery is so challenging: peptides must survive digestion and reach the bloodstream in sufficient quantities to have an effect.[3]

The hypothalamic-pituitary axis

The hypothalamus and pituitary gland together produce at least 15 peptide hormones that serve as the brain's master control system for the rest of the endocrine system.

Hypothalamic releasing and inhibiting hormones

The hypothalamus produces small peptides that travel through the hypophyseal portal system to regulate the anterior pituitary:

  • GnRH (gonadotropin-releasing hormone, 10 amino acids): triggers release of LH and FSH, controlling reproductive function. GnRH agonists and antagonists are used therapeutically for prostate cancer, endometriosis, and IVF.
  • TRH (thyrotropin-releasing hormone, 3 amino acids): the smallest peptide hormone, stimulates TSH release. Also stimulates prolactin secretion.
  • CRH (corticotropin-releasing hormone, 41 amino acids): drives the stress response by stimulating ACTH release. Central to the hypothalamic-pituitary-adrenal (HPA) axis.
  • GHRH (growth hormone-releasing hormone, 44 amino acids): stimulates growth hormone secretion. GHRH analogs like sermorelin and tesamorelin are used therapeutically.
  • Somatostatin (14 or 28 amino acids): inhibits growth hormone, TSH, insulin, and glucagon release. Octreotide and lanreotide are synthetic somatostatin analogs used for acromegaly and neuroendocrine tumors.

Posterior pituitary hormones

  • Oxytocin (9 amino acids): triggers uterine contractions during labor and milk letdown during nursing. Also involved in social bonding, trust, and cardiovascular protection.[4]
  • Vasopressin/ADH (9 amino acids): regulates water reabsorption in the kidneys and vasoconstriction. Desmopressin, a synthetic analog, treats diabetes insipidus and bedwetting.

Anterior pituitary hormones

  • Growth hormone (191 amino acids): stimulates growth and metabolism through IGF-1. Deficiency causes dwarfism; excess causes acromegaly.
  • ACTH (39 amino acids): stimulates cortisol production by the adrenal glands. Elevated in Addison's disease, suppressed in Cushing's syndrome.
  • Prolactin (199 amino acids): drives milk production. The only pituitary hormone under tonic inhibitory control (by dopamine).
  • TSH (glycoprotein, ~211 amino acids combined): stimulates thyroid hormone production.
  • FSH and LH (glycoprotein hormones): control gonadal function and reproductive cycling.

Pancreatic peptide hormones

The islets of Langerhans contain four cell types, each producing a distinct peptide hormone:

  • Insulin (51 amino acids, from beta cells): the only hormone that lowers blood glucose. Insulin deficiency or resistance causes diabetes mellitus. More insulin analogs exist than any other peptide drug class.
  • Glucagon (29 amino acids, from alpha cells): raises blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis. Acts as insulin's counterregulatory partner. Glucagon is also being explored as part of multi-agonist drugs like tirzepatide and retatrutide.
  • Somatostatin (from delta cells): locally inhibits both insulin and glucagon secretion, fine-tuning islet output.
  • Pancreatic polypeptide (36 amino acids, from PP cells): reduces appetite and gastric emptying. Its physiological role is less well characterized than insulin or glucagon.
  • Amylin/IAPP (37 amino acids, co-secreted with insulin from beta cells): slows gastric emptying, suppresses glucagon, and promotes satiety. Pramlintide (Symlin) is a synthetic analog. Amylin is also the basis for cagrilintide, a component of CagriSema.

Gut peptide hormones

The gastrointestinal tract is the largest endocrine organ in the body by sheer number of hormone-producing cells. Over 20 peptide hormones are produced by enteroendocrine cells distributed along the gut lining.

Incretins:

  • GLP-1 (glucagon-like peptide-1, 30 amino acids): secreted by L-cells in the ileum and colon after meals. Enhances insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite. Native half-life is approximately 2 minutes due to DPP4 cleavage. Six GLP-1 receptor agonist drugs are now FDA-approved, representing the most successful class of peptide-derived drugs in history.[5]
  • GIP (glucose-dependent insulinotropic polypeptide, 42 amino acids): secreted by K-cells in the duodenum. The other incretin hormone. GIP receptor agonism is combined with GLP-1 agonism in tirzepatide.

Appetite and satiety peptides:

  • Ghrelin (28 amino acids): the only known orexigenic (appetite-stimulating) gut hormone, secreted by the stomach before meals. Ghrelin levels rise before meals and fall after eating. Ghrelin also stimulates growth hormone release through the GHS-R1A receptor.[6]
  • CCK (cholecystokinin, 8-58 amino acids): secreted by I-cells in response to fat and protein. Triggers gallbladder contraction, pancreatic enzyme secretion, and satiety signaling.
  • PYY (peptide YY, 36 amino acids): secreted by L-cells after meals. Reduces appetite through hypothalamic Y2 receptors. The "ileal brake" mechanism.

Digestive regulation:

  • Secretin (27 amino acids): the first hormone ever discovered (1902). Stimulates bicarbonate secretion from the pancreas to neutralize stomach acid in the duodenum.
  • Gastrin (17-34 amino acids): stimulates gastric acid secretion. Zollinger-Ellison syndrome results from gastrin-producing tumors.
  • Motilin (22 amino acids): triggers the migrating motor complex, the "housekeeper" contractions that sweep the small intestine between meals.
  • VIP (vasoactive intestinal peptide, 28 amino acids): relaxes smooth muscle, stimulates water and electrolyte secretion, and acts as a neurotransmitter in the enteric nervous system.

For how these hormones coordinate appetite signaling between the gut and the brain, see brain vs gut: how peptides coordinate appetite.

Cardiovascular peptide hormones

The heart and blood vessels produce peptide hormones that regulate blood pressure and fluid balance:

  • ANP (atrial natriuretic peptide, 28 amino acids): released by atrial cardiomyocytes in response to volume expansion. Promotes natriuresis and vasodilation, lowering blood pressure. See our detailed article on ANP.
  • BNP (B-type natriuretic peptide, 32 amino acids): released by ventricular cardiomyocytes under wall stress. BNP and its inactive fragment NT-proBNP are the primary biomarkers for heart failure diagnosis.[7] See BNP and NT-proBNP.
  • Endothelin-1 (21 amino acids): the most potent endogenous vasoconstrictor. Produced by endothelial cells. Endothelin receptor antagonists (bosentan, ambrisentan) treat pulmonary arterial hypertension.
  • Angiotensin II (8 amino acids): vasoconstrictor and aldosterone secretagogue produced by the renin-angiotensin system. ACE inhibitors and ARBs, among the most prescribed drug classes globally, work by blocking angiotensin II's production or action. See angiotensin II.
  • Adrenomedullin (52 amino acids): vasodilator and cardioprotective peptide. Elevated in heart failure and sepsis as a compensatory mechanism.[1]

Adipose tissue peptide hormones

Fat tissue is now recognized as a major endocrine organ. Adipokines produced by adipocytes regulate metabolism, inflammation, and appetite:

  • Leptin (167 amino acids): the "satiety hormone" secreted in proportion to fat mass. Signals to the hypothalamus to reduce appetite. Leptin resistance, where the brain stops responding to elevated leptin, is a hallmark of obesity.
  • Adiponectin (244 amino acids): improves insulin sensitivity and has anti-inflammatory effects. Levels decrease with increasing adiposity, which is paradoxical: more fat tissue produces less of this protective hormone.
  • Resistin (108 amino acids): linked to insulin resistance in animal models, though its role in humans is more nuanced and primarily involves inflammatory regulation.

Brain and nervous system peptide hormones

Neuropeptides function as neurotransmitters, neuromodulators, or both:

  • Endorphins (beta-endorphin is 31 amino acids): endogenous opioid peptides that modulate pain perception, reward, and stress responses. The "runner's high" involves endorphin and endocannabinoid release.
  • Enkephalins (5 amino acids each, met- and leu-): the first endogenous opioids discovered (1975). Act at mu and delta opioid receptors.
  • Substance P (11 amino acids): mediates pain transmission and inflammatory responses. Neurokinin-1 receptor antagonists (aprepitant) treat chemotherapy-induced nausea.
  • Neuropeptide Y (36 amino acids): the most abundant neuropeptide in the brain. Stimulates appetite, reduces anxiety, regulates circadian rhythms, and modulates cardiovascular function.[8]
  • CGRP (calcitonin gene-related peptide, 37 amino acids): potent vasodilator involved in migraine pathophysiology. CGRP-targeting monoclonal antibodies (erenumab, fremanezumab, galcanezumab) have transformed migraine prevention.
  • Orexin/Hypocretin (33-28 amino acids): regulates wakefulness and arousal. Orexin deficiency causes narcolepsy. Dual orexin receptor antagonists (suvorexant, lemborexant) treat insomnia.

Other peptide hormones

Several additional peptide hormones do not fit neatly into organ-system categories:

  • Erythropoietin (165 amino acids): produced by the kidneys in response to hypoxia. Stimulates red blood cell production. Recombinant EPO treats anemia and has been notoriously abused in endurance sports.
  • Calcitonin (32 amino acids): produced by thyroid C-cells. Lowers blood calcium by inhibiting osteoclast activity. Salmon calcitonin is used therapeutically for osteoporosis and Paget's disease.
  • Parathyroid hormone (84 amino acids): raises blood calcium through bone resorption, renal calcium reabsorption, and vitamin D activation. Teriparatide (PTH 1-34) treats osteoporosis by stimulating bone formation when given intermittently.
  • Thymosin alpha-1 (28 amino acids): immune-modulating peptide from the thymus. Approved in several countries for hepatitis B and used as an immune adjuvant.

From hormones to drugs

The therapeutic peptide industry is built on endogenous peptide hormones. Nearly every major peptide drug class derives from a naturally occurring hormone:[9]

  • Insulin analogs from insulin
  • GLP-1 receptor agonists from GLP-1[10]
  • Somatostatin analogs from somatostatin
  • GnRH agonists/antagonists from GnRH
  • CGRP antibodies targeting CGRP
  • Natriuretic peptide (nesiritide) from BNP
  • PTH analogs from parathyroid hormone

The pattern is consistent: identify the endogenous peptide, characterize its receptor, then engineer a modified version with improved stability, potency, or selectivity. The rapid degradation that makes endogenous peptide hormones precise also makes them poor drugs, requiring structural modifications (albumin binding, PEGylation, fatty acid conjugation, amino acid substitutions) to extend their half-lives from minutes to days or weeks.

The Bottom Line

The human body produces dozens of peptide hormones from at least 10 organ systems, controlling blood sugar, blood pressure, appetite, growth, reproduction, pain, and immune function. These hormones share common features: water solubility, receptor-mediated signaling, and rapid enzymatic degradation. The endogenous peptide hormone repertoire has served as the primary source for therapeutic peptide drug development, with modified versions of insulin, GLP-1, somatostatin, GnRH, and others now treating millions of patients worldwide.

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